1. Field of the Invention
The present invention relates generally to display devices and particularly to a method of modifying image signals in the devices.
2. Description of Related Art
A liquid crystal display (LCD) includes a pair of panels with field generating electrodes and a liquid crystal layer with dielectric anisotropy disposed between the two panels. An electric field is formed in the liquid crystal layer using the electrodes, and the transmittance of light passing through the liquid crystal layer is adjusted by controlling the electric field, thereby obtaining the desired images.
A pair of electrodes that generate electric field in cooperation with each other and the liquid crystal layer disposed therebetween form a liquid crystal capacitor. The strength of the electric field applied to the liquid crystal layer can be controlled by adjusting the voltage across the liquid crystal capacitor. The application of the voltage across the liquid crystal capacitor is performed by scanning for a given time.
However, the response time of liquid crystal molecules in reaction to the applied electric field is long. Thus, sometimes, it takes time for the liquid crystal capacitor to charge to a target voltage, with the exact time depending on the difference between the previous voltage and the target voltage. When the difference between the target voltage and the previous voltage is large, the liquid crystal capacitor may not reach the target voltage for a long time.
One of the solutions suggested for addressing the problem of long liquid crystal layer charge time is dynamic capacitance compensation (DCC). The DCC method entails applying a voltage that is higher than a target voltage to the liquid crystal capacitor to take advantage of fact that the response time decreases as the voltage across the liquid crystal capacitor increases. To determine the modified voltage that is applied to the liquid crystal capacitor, the DCC method converts digital image signals to analog voltages by using a lookup table. The lookup table stores the values that can be used to determine the modified voltage. One disadvantage with the lookup table is that if it is large, it could result in an increased size of the display device. Thus, the size of the lookup table needs to be small to maintain the compactness of the LCD.
FIG. 1 is an illustration of an exemplary wire frame created by using a computer aided design (CAD) program and shown on an LCD screen. A wire frame is a set of line segments representing a three dimensional object. The exemplary wire frame of FIG. 1 represents a kettle. Sometimes, when the wire frame is moved on the screen or zoomed in or out, some flickering is seen on the screen. This flickering phenomenon, called “wire frame flickering,” is particularly severe in a patterned vertically aligned (PVA) mode LCD having cutouts at the field generating electrodes.
As the wire frame flickering phenomenon compromises display quality, an improved display quality can be achieved by reducing the phenomenon.